1. Field of the Invention
This invention relates to an organic luminescent device, and more particularly to a device which emits light upon application of an electric field to a thin film formed of an organic compound.
2. Related Background Art
The organic luminescent device is a device in which a thin film containing a fluorescent organic compound is held between an anode and a cathode, electrons and holes are injected from each electrode to produce excitons of the fluorescent organic compound, and the light is utilized that is emitted when the excitons return to the ground state.
In research made by Eastman Kodak Company in 1987 (Appl. Phys. Lett. 51, 913, 1987), a function-separated double-layer structure device is reported in which ITO (indium-tin-oxide) is used as an anode and an alloy of magnesium and silver is used as a cathode, where an aluminum quinolinol complex is used as an electron transporting material and a luminescent material, and a triphenylamine derivative is used as a hole transporting material, which device enables light of about 1,000 cd/m2 to be emitted under application of a voltage of about 10 V. Related patents may include U.S. Pat. Nos. 4,539,507, 4,720,432 and 4,885,211.
By changing types of the fluorescent organic compound, emission from ultlaviolet up to infrared light is possible, and various compounds are recently energetically researched. For example, they are disclosed in U.S. Pat. Nos. 5,151,629, 5,409,783 and 5,382,477, and Japanese Patent Application Laid-Open Nos. H02-247278, H03-255190, H05-202356, H09-202878 and H09-227576.
Besides the organic luminescent devices making use of low-molecular weight materials as mentioned above, an organic emission-device making use of a conjugated type high-molecular material is further reported by a group of members of Cambridge University (Nature, 347, 539, 1990). In this report, polyphenylene vinylene (PPV) is formed into a film by a coating system to ascertain luminescence in a single layer. Related patents of such a conjugated type high-molecular material may include U.S. Pat. Nos. 5,247,190, 5,514,878 and 5,672,678, and Japanese Patent Application Laid-Open Nos. H04-145192 and H05-247460.
A phosphorescent organic luminescent device making use of an iridium complex such as Ir(ppy)3 as a luminescent material (Appl. Phys. Lett. 75, 4, 1999) also has lately attracted attention, and a high emission efficiency is reported.
Recent advance in organic luminescent devices is noticeable, which are characterized by high luminance at a low applied voltage, variety of luminescence wavelengths, high-speed response, and thin-gage and light-weight, and hence they suggest possibility for extensive uses. However, there are many problems in durability such as changes over time in long-time use and deterioration due to oxygen-containing atmospheric gas or moisture. Where their application to full-color display and the like is taking into account, blue, green and red luminescence with much longer lifetime, higher conversion efficiency and higher color purity is required under the existing conditions.
As an example of materials containing an anthracene ring and organic luminescent devices, Japanese Patent Application Laid-Open No. H08-012600 discloses a phenyl anthracene derivative. This reports that a good organic film can be formed because of low crystallizability especially when used as a blue luminescent material or an electron transporting material. However, its luminescence efficiency and durability lifetime have been insufficient in practical use.
As another example, Japanese Patent Application Laid-Open Nos. H09-157643 and H10-072579 disclose an amino anthracene derivative and a diamino anthracene derivative, respectively. They report that green luminescence is obtained when used as a luminescent material. However, the device has a low luminescence efficiency, and also has been insufficient in practical use in regard to durability lifetime.
As still another example, Japanese Patent No. 3,008,897 discloses a device making use of a specific bianthryl compound as a luminescent material, which, however, has no disclosure in regard to luminescence efficiency and durability lifetime.
As a further example, Japanese Patent Application Laid-Open No. H11-008068 discloses a device making use of, as a luminescent material, a specific anthracene compound containing an olefin moiety, and reports that luminescence of from yellow light to red light is obtained. It, however, has been insufficient in practical use in regard to luminescence efficiency.
As a still further example, Japanese Patent Application Laid-Open No. 2001-284050 discloses a device having a luminescent medium layer which contains an anthracene derivative with a specific structure, an electron transporting compound and another luminescent compound. This reports that a red luminescent device improved in reliability is obtained. However, the device has an insufficient luminescence efficiency in practical use, and also it has been difficult to obtain blue luminescence because of device structure.